Microphone



Patented July 3l, 1928.

UNITE JOSEPH E. AIKEN, OF WILKINSBUBG, PENNSYLVANIA, ASSIGNOR TOWESTINGHOUSE ELECTRIC 8a MANUFACTURING COMPANY, A CORPORATION OFPENNSYLVANIA.

MICROPHONE.

Application filed June 17,

My invention relates to microphones and it has particular relation tomicrophones of the pick-up type.

One object of my invention is to produce an improved microphone for usein connection with the transmission of announcements of public events. Y

Another object of my invention is to produce a microphone device andsound controlling means combined therewith whereby a preferentialresponse to sound from a predetermined Vsource can be obtained from themicrophone.

Anotherobject of my invention is to produce a microphone structure thatis responsive only to a single predetermined sound source and which can,therefore, be operated satisfactorily in a noisy place.

Another object of my invention is to produce a microphone device that isresponsive to a singl'e speakers voice and which can, therefore, beoperated in a noisy location without interference from extraneousnoises.

In the prior art of the construction and operation of microphonedevices, it has been found that they respond substantially in aproportional manner to the intensity of any sound impinging upon theirdiaphragms.

lVhen it is desired to obtain a translation of the vibratory motionproduced by sound waves into vibratory electric currents, such as isdesired for a sound pick-up to be used for the radio broadcasting ofperformances, much difficulty has been experienced in obtaining aresponse to the desired sounds and in avoiding response to extraneoussounds such as are produced by an audience, or by echoes of the sourcewhich it is desired to copy.

Particular difficulty has been experienced when it was desired tobroadcast the voice of an announcer describing plays at an athleticevent, such as a football game or a boxing match, where the cheering ofthe spectators produced a sound much greater in volume than the sound ofthe announcers voice.

Microphones constructed according to the prior art have been found to beentirely impracticable under such conditions because of the fact that anannouncers voice is entirely lost in the extraneous sounds.

My invention provides means whereby the 1924;. Serial No. 720,477.

microphone is caused to respond to an announcers voice only, and isprevented from responding to extraneous sounds such as cheering.

Other objects and structural details of my invention will be apparentfrom the following description when read in connection with theaccompanying drawings, wherein:

.Figure 1 is a perspective view of the device of my invention;

Fig. 2 is a horizontal sectional view of the microphone Fig. 3 is aview, partially in elevation and partially in section, of themicrophone, and

Fig. el is a sketch in elevation of the microphone in operative relationto a speaker.

Referring to Fig. 1, a metallic cylinder 1,

preferably of steel, is mounted upon a stand 2. The cylinder l hasperforated metal closures 3 and 3 at its ends. An aperture d is providedat substantially the central portion of the cylinder 1. n A cylindricalfelt or other sound absorbing lining 5 is provided within the cylinder1, and felt discs 6 and 6 are placed within the perforated metalclosures 3 and 3. A double-button microphone 7 is shown within both thecylinder 1 and the lining 5. The microphone 7 comprises a frame 8, adiaphragm 9, granule containers 11 and 12 and supporting bridges 14 and15 therefor. The microphone 7 is further mounted in a supporting frame1G which is slidably mounted within the cylinders 1 and 5.

In Fig. 2, a double-button microphone is shown and described by way ofexample. Such a double-button microphone is not, however, essential,since I have found that any microphone which has both sides of itsdiaphragm exposed to sound waves is satisfactory.

Reference may now be had to Fig. 3 in which part of the cylinder hasbeen broken away to show elastic supporting cords 17, 18, 19 and 2O forsustaining the microphone 7 within the frame 16.

In the operation of my device, extraneous sounds coming from randomdirections, as indicated by the arrow 21, (Fig. 2) are reflected fromthe smooth surface of cylinder 1, as shown by the arrow 22. Thisreflection occurs with all sounds, except such sounds as strike normalto the surface of the cylinder 1, as shown by the arrow 23 (Fig. 2)which sound is conveyed through the body of the cylinder 1 to the feltlining 5 by which it is absorbed and destroyed. Sound from anotherdirection such as indicated by the arrow 24 may enter the end ofcylinder 1 through the perforated closure 3 and impinge upon microphone7. Such sound does not, however, influence microphone 7 to produce aresponse, since the sound waves represented by arrows 24, being inphase, infinence both sides of diaphragm 9 equally at a given instant,and, therefore, produce no vibration of diaphragm 9. rlhere being novibration corresponding to such sound, there can be no response by thediaphragm to such sound.

A sound from a speaker, such as that sound represented by arrow 25,enters through aperture 4 and impinges upon one side only of thediaphragm 9, thereby producing vibration of the diaphragm 9 andtherefore a response. A sound from a speaker entering through aperture4, such as that represented by arrow 26, which does not strike thediaphragm 9 is absorbed and destroyed by the felt lining 5 and, notbeing reflected, does not produce vibration of diaphragm 9 and thereforeis without effect.

The edges of the aperture 4 conform to a speakers face. riChis featureenables the speaker to place his mouth within the aperture, therebyfilling it completely and preventing the ingress of extraneous soundsthrough aperture 4. The perforations of the end closures 3 and 3 allowthe speakers breath free egress from the cylinder.

The amplitude of the response of microphone 7 to the speakers voice maybe controlled by shifting it lengthwise along the axis of cylinder l. ffplaced directly opposite the aperture 4, a maximum response is obtained,since the direct path of sound wave causes it to impinge upon diaphragm9. Vhen a lesser amplitude of response is desired, the microphone T maybe moved to a position not immediately in front of aperture 4. Thegreater distance then reduces the intensity of the sound striking thediaphragm by the inverse square factor and also allows the same sound,by the bending of the wave front around the edge of the frame 8, toinfluence the reverse side of diaphragm 9, thereby neutralizing aportion of the influence produced by sound upon the forward side of thediaphragm 9. By this means, it is possible to control the amplitude ofthe response obtained by the microphone, as well as to prevent responseof the microphone to extraneous sounds.

The effect of mechanical impact and vibrations of the structure uponwhich the complete device is supported, which impact,

if allowed free access to the device, would produce undesiredfiuctuations in the microphone currents, is prevented from influencingthe microphone by an elastic supporting means, represented by the rubbercords 17, 18, 19 and 2O which support the microphone 7 within the frame16.

By this means, l am able to obtain a maximum, or an optimum, responce ofa microphone to a speakers voice to prevent response of said microphoneto other and extraneous sounds of greater magnitude than the speakersvoice.

wWhile l have Shown only one embodiment of my invention in theaccompanying drawings, it is capable of various changes andmodifications without departing from the spirit thereof, and it isdesired, therefore, that only such limitations shall be placed thereonas are imposed by the prior art or set forth in the appended claims.

l claim as my invention:

l. ln combination, nncmicrophone and sound-shielding means thereforcomprising a`s`ii`n reflecting cylinder having a side aperture, asound-absorbing liningYA therefor, and sound-absorbent closures for theends of said cylinder, said microphone being adjustably suppertedmwithin.Said cylinder,

2. In combination, a microphone device having a diaphragm, both sides ofwhich are exposed to sound, and sound-directive means comprising anapertured cylinder, a sound-absorbing lining therefor and soundabsorbentclosures for the ends thereof, said microphone being flexibly mountedtherein.

3. fn combination, a microphone device having a diaphragm exposed onboth sides to sound, and sound-directive means comprising an aperturedcylinder, a sound-absorbing lining thereto and sound-absorbent closuresfor the ends thereof, said/microphone..being` flexibly mounted thereinwith the plane of the diaphragm thereof parallel to the axis of saidcylinder.

4. ln combination, a microphone device having a diaphragm exposed onboth sides to sound, and sound directive means comprising an aperturedcylinder, a sound-absorbing lining therefor and sound absorbent closuresfor the ends thereof, said microphone being flexibly mounted thereinadjacent to said aperture.

5. In a. sound translating device, a tubular shield for confiningextraneous sounds to directions along the tube, said shield having alateral opening for the admission of sound from a given source and asoundresponsive device including a diaphragm within the shield andparallel to the length thereof.

In testimony whereof, l have hereunto subscribed my naine this 3rd dayof June,

JOSEPH E. AKEN.

